Several references, cited at the end of this patent specification, are identified by numbers in square brackets in the description below and are hereby incorporated by reference.
THz radiation typically denotes electromagnetic energy in an ITU-designated band of frequencies from 0.3 to 3 terahertz (1 THz=1012 Hz) and wavelengths ranging from 1 mm to 0.1 mm (100 μm). This is a range between microwaves and infrared light, and shares some properties with each. Like infrared and microwave radiation, THz radiation is understood to travel in a line-of-sight and to be non-ionizing, which makes it safer for biological tissue. Like microwave radiation, THz radiation can pass through some non-conducting materials such as clothing, paper, cardboard, wood, masonry, plastic, and ceramics. THz radiation can be modulated by differences in water content and density of tissue and therefore can be used for imaging. Some materials of interest in various fields, including security, have spectral “fingerprints” in the THz range, which opens prospects for combining spectral identification with imaging. The short wavelength of THz radiation can contribute to high spatial resolution in imaging and to high bandwidth in communications.
Despite such potential advantages of THz radiation, progress in utilizing it has been hindered by difficulties in detecting such radiation. Known THz detectors include pyroelectric sensors, Schottky barrier diodes, and GaAs field-effect transistors. The known detectors have limitations such as low sensitivity, slow speed, requirements for cryogenic cooling, and difficulty scaling to array formats suitable for THz imaging. Proposals have been made for using CMOS transistors but in modes that suffer from low efficiency particularly at higher frequencies. Infrared focal plane arrays (FPAs) have been proposed for THz imaging experiments but the detection efficiency is believed low, typically less than 5%. Researchers have explored metamaterlal (MM) devices, which are sub-wavelength elements in which their structure rather than their composition dominates their electromagnetic properties. MMs have been proposed for creating resonant absorber structures. Plasmonic devices have been proposed for use in surface plasmon resonance (SPR), where incident light resonantly couples with surface plasmons at a metal/dielectric interface.
The challenge of discovering efficient and effective THz detectors has remained for a long time. This patent specification is directed to meeting that challenge and providing advantageous systems utilizing novel THz detectors.